The present invention relates to a hybrid compressor that is used mainly for a vehicular air-conditioning device and driven selectively by an engine or an electric motor, and its control device.
In a typical vehicular air-conditioning device, cooling cannot be executed when the engine driving the vehicle is stopped. Recently, vehicles have been developed that stop the engine when the vehicle is temporarily stopped. Further, in another new type of vehicle, the engine may be stopped even while the vehicle is traveling, depending on conditions. In these vehicles, a hybrid compressor is used for comfortably cooling the passenger cabin. The hybrid compressor is driven by the engine while the engine is running by an electric motor when the engine is stopped.
One hybrid compressor and its controlling method is disclosed in JP-A-2000-110734. This hybrid compressor is furnished with a compression mechanism having a rotating shaft, an electric motor having an output shaft connected with the rotating shaft, and an electromagnetic clutch connected with the output shaft. An engine is connected with the output shaft through the electromagnetic clutch. When the engine is in an operating state and the electromagnetic clutch is turned on, the driving force of the engine is transmitted through the output shaft to the rotating shaft so that the compression mechanism can be driven. By contrast, when the engine is stopped, the electromagnetic clutch is turned off, and the output shaft and the rotating shaft are disconnected from the engine, the electric motor drives the compression mechanism using the electric power of a battery.
Furthermore, in the above hybrid compressor, a swash-plate type externally variable displacement compressor is adopted. In this compressor, a piston is driven by the rotation of a swash plate, and a displacement adjusting mechanism is externally adjusted, so that a certain displacement can be obtained by varying of the inclination angle of the swash plate. In order to constantly optimize the cooling performance in a refrigerating circuit, the inclination angle of the swash plate is adjusted based on the cooling load so that the discharge displacement can be controlled.
The applicant of the present invention discloses, in JP-A-H10-291415, a method for enabling a motor of a hybrid compressor to be reduced in size and mounted on a vehicle. In this hybrid compressor, the load of the motor is set to zero when the motor is turned on. The load of the motor is then increased after rotation of the motor becomes stable.
However, in the above case, it takes an interval to return to the required displacement after the displacement is once shifted to zero. In particular, when heat capacity is low and the target cooling temperature is low, it takes a longer interval to return to the required displacement. This inhibits the air-conditioning and reduces passenger comfort for the interval.